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Message-ID: <38891bc8-3550-403c-88d7-2e4058bbe20c@linux.microsoft.com>
Date: Mon, 14 Aug 2023 10:30:30 +0200
From: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
To: Dan Williams <dan.j.williams@...el.com>, linux-coco@...ts.linux.dev
Cc: Borislav Petkov <bp@...en8.de>,
Tom Lendacky <thomas.lendacky@....com>,
Dionna Glaze <dionnaglaze@...gle.com>,
Brijesh Singh <brijesh.singh@....com>, peterz@...radead.org,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] virt: sevguest: Add TSM_REPORTS support for
SNP_{GET, GET_EXT}_REPORT
On 8/14/2023 9:43 AM, Dan Williams wrote:
> The sevguest driver was a first mover in the confidential computing
> space. As a first mover that afforded some leeway to build the driver
> without concern for common infrastructure.
>
> Now that sevguest is no longer a singleton [1] the common operation of
> building and transmitting attestation report blobs can / should be made
> common. In this model the so called "TSM-provider" implementations can
> share a common envelope ABI even if the contents of that envelope remain
> vendor-specific. When / if the industry agrees on an attestation record
> format, that definition can also fit in the same ABI. In the meantime
> the kernel's maintenance burden is reduced and collaboration on the
> commons is increased.
>
> Convert sevguest to use CONFIG_TSM_REPORTS to retrieve the blobs that
> the SNP_{GET,GET_EXT}_REPORT ioctls produce. An example flow for
> retrieving the SNP_GET_REPORT blob via the TSM interface utility,
> assuming no nonce and VMPL==2:
>
> echo 2 > /sys/class/tsm/tsm0/privlevel
> dd if=/dev/urandom bs=64 count=1 | xxd -p -c 0 > /sys/class/tsm/tsm0/inhex
> hexdump -C /sys/class/tsm/tsm0/outblob
>
> ...while the SNP_GET_EXT_REPORT flow needs to additionally set the
> format to "extended":
>
> echo 2 > /sys/class/tsm/tsm0/privlevel
> echo extended > /sys/class/tsm/tsm0/format
> dd if=/dev/urandom bs=64 count=1 | xxd -p -c 0 > /sys/class/tsm/tsm0/inhex
> hexdump -C /sys/class/tsm/tsm0/outblob
>
> The old ioctls can be lazily deprecated, the main motivation of this
> effort is to stop the proliferation of new ioctls, and to increase
> cross-vendor colloboration.
>
> Note, only compile-tested.
>
> Link: http://lore.kernel.org/r/64961c3baf8ce_142af829436@dwillia2-xfh.jf.intel.com.notmuch [1]
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Dionna Glaze <dionnaglaze@...gle.com>
> Cc: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
> drivers/virt/coco/sev-guest/Kconfig | 1
> drivers/virt/coco/sev-guest/sev-guest.c | 81 +++++++++++++++++++++++++++++++
> 2 files changed, 82 insertions(+)
>
> diff --git a/drivers/virt/coco/sev-guest/Kconfig b/drivers/virt/coco/sev-guest/Kconfig
> index da2d7ca531f0..1cffc72c41cb 100644
> --- a/drivers/virt/coco/sev-guest/Kconfig
> +++ b/drivers/virt/coco/sev-guest/Kconfig
> @@ -5,6 +5,7 @@ config SEV_GUEST
> select CRYPTO
> select CRYPTO_AEAD2
> select CRYPTO_GCM
> + select TSM_REPORTS
> help
> SEV-SNP firmware provides the guest a mechanism to communicate with
> the PSP without risk from a malicious hypervisor who wishes to read,
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index f48c4764a7a2..5941081502e8 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -16,6 +16,7 @@
> #include <linux/miscdevice.h>
> #include <linux/set_memory.h>
> #include <linux/fs.h>
> +#include <linux/tsm.h>
> #include <crypto/aead.h>
> #include <linux/scatterlist.h>
> #include <linux/psp-sev.h>
> @@ -769,6 +770,78 @@ static u8 *get_vmpck(int id, struct snp_secrets_page_layout *layout, u32 **seqno
> return key;
> }
>
> +static u8 *sev_report_new(struct device *dev, const struct tsm_desc *desc,
> + size_t *outblob_len)
get_report and get_ext_report both have a:
lockdep_assert_held(&snp_cmd_mutex);
so you'd need to take that lock somewhere here.
Jeremi
> +{
> + struct snp_guest_dev *snp_dev = dev_get_drvdata(dev);
> + const int report_size = SZ_16K;
> + const int ext_size = SZ_16K;
> + int ret, size;
> +
> + if (desc->inblob_len != 64)
> + return ERR_PTR(-EINVAL);
> +
> + if (desc->outblob_format == TSM_FORMAT_EXTENDED)
> + size = report_size + ext_size;
> + else
> + size = report_size;
> +
> + u8 *buf __free(kvfree) = kvzalloc(size, GFP_KERNEL);
> +
> + if (desc->outblob_format == TSM_FORMAT_EXTENDED) {
> + struct snp_ext_report_req ext_req = {
> + .data = { .vmpl = desc->privlevel },
> + .certs_address = (__u64)buf + report_size,
> + .certs_len = ext_size,
> + };
> + memcpy(&ext_req.data.user_data, desc->inblob, desc->inblob_len);
> +
> + struct snp_guest_request_ioctl input = {
> + .msg_version = 1,
> + .req_data = (__u64)&ext_req,
> + .resp_data = (__u64)buf,
> + };
> +
> + ret = get_ext_report(snp_dev, &input, SNP_KARG);
> + } else {
> + struct snp_report_req req = {
> + .vmpl = desc->privlevel,
> + };
> + memcpy(&req.user_data, desc->inblob, desc->inblob_len);
> +
> + struct snp_guest_request_ioctl input = {
> + .msg_version = 1,
> + .req_data = (__u64) &req,
> + .resp_data = (__u64) buf,
> + };
> +
> + ret = get_report(snp_dev, &input, SNP_KARG);
> + }
> +
> + if (ret)
> + return ERR_PTR(ret);
> +
> + *outblob_len = size;
> + no_free_ptr(buf);
> + return buf;
> +}
> +
> +static const struct tsm_ops sev_tsm_ops = {
> + .name = KBUILD_MODNAME,
> + .report_new = sev_report_new,
> +};
> +
> +static const struct attribute_group *sev_tsm_attribute_groups[] = {
> + &tsm_default_attribute_group,
> + &tsm_extra_attribute_group,
> + NULL,
> +};
> +
> +static void unregister_sev_tsm(void *data)
> +{
> + unregister_tsm(&sev_tsm_ops);
> +}
> +
> static int __init sev_guest_probe(struct platform_device *pdev)
> {
> struct snp_secrets_page_layout *layout;
> @@ -842,6 +915,14 @@ static int __init sev_guest_probe(struct platform_device *pdev)
> snp_dev->input.resp_gpa = __pa(snp_dev->response);
> snp_dev->input.data_gpa = __pa(snp_dev->certs_data);
>
> + ret = register_tsm(&sev_tsm_ops, &pdev->dev, sev_tsm_attribute_groups);
> + if (ret)
> + goto e_free_cert_data;
> +
> + ret = devm_add_action_or_reset(&pdev->dev, unregister_sev_tsm, NULL);
> + if (ret)
> + goto e_free_cert_data;
> +
> ret = misc_register(misc);
> if (ret)
> goto e_free_cert_data;
>
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